block RFC-1918 by ipfw2

RFC-1918, the private block
these IP address should be stopped on the outside interface, except when they responses to traceroute and some type of ICMP.

${fwcmd} table 1 flush
${fwcmd} table 1 add 10.0.0.0/8
${fwcmd} table 1 add 172.16.0.0/12
${fwcmd} table 1 add 192.168.0.0/16
${fwcmd} add deny all from 'table(1)' to   any in via ${oif}